Traceable high accuracy gas mixtures for biogas analysis
Biogas and biomethane are becoming an increasingly important means to delivering a sustainable, low carbon energy future. Renewable energy targets have driven significant growth in the biogas economy, as biomethane can be blended with natural gas in existing transmission networks and used to power vehicles.
Multi-component standards are available, including, but not limited to, the components and ranges in the table below. UKAS accreditation is also available for the majority of components.
Component
|
Amount fraction range
(cmol/mol)
|
Uncertainty
(k=2) (% rel.)
|
| Methane |
40 – 99.9 |
≤ 0.2 |
| Carbon dioxide |
0.04 – 55 |
≤ 0.2 |
| Nitrogen |
0.02 – 25 |
≤ 0.2 |
| Hydrogen |
0.05 – 2 |
≤ 1.0 |
| Oxygen |
0.05 – 2 |
≤ 1.0 |
Mixtures containing additional components not listed may also be available on request.
Biogas impurities
Raw biogas contains a diverse range of impurities, which vary in amount fraction depending on the source material used. A European specification is being developed that will impose maximum limit values on the impurities found within upgraded biogas and biomethane. NPL's gas reference standards are being used to directly support the development of the biogas economy.
Siloxanes
Siloxane impurities within biogas cause damage to processing equipment when combusted, even at trace-levels. NPL offers traceable gas standards containing the most common siloxanes found in biogas. The table provides typical values for amount fraction ranges and uncertainties, based on over six years of research and development.
Molecular structure of L2, L3, D4 and D5 siloxanes
(C: black, H: white, O: red, Si: teal)
Component
|
Amount fraction range (µmol/mol)
|
Relative Uncertainty (%)
|
Matrix
|
| L2 (Hexamethyldisiloxane) |
0.025 – 200 |
1 – 3 |
Biogas, Methane or Nitrogen
|
| L3 (Octamethyltrisiloxane) |
0.004 – 100 |
1 – 10 |
| D4 (Octamethylcyclotetrasiloxane) |
0.085 – 55 |
1 – 7 |
| D5 (Decamethylcyclopentasiloxane) |
0.006 – 10 |
2 – 10 |
Sulphur species
Depending on the nature of the substrate, the anaerobic digestion process produces sulphur-containing compounds ranging from ppb levels to several thousands of ppm. NPL offers traceable reference standards of binary and multi-component sulphur compounds within biogas. UKAS accreditation is available for matrices of methane and nitrogen.
Component
|
Amount fraction range (µmol/mol)
|
Relative Uncertainty (%)
|
Matrix
|
| Hydrogen sulphide |
0.4 to 5000 |
2 - 5 |
Biogas, Methane or Nitrogen
|
| Carbonyl sulphide |
0.4 to 5000 |
2 - 5 |
| Carbon disulphide |
0.4 to 200 |
2 - 5 |
| Dimethyl sulphide |
0.4 to 200 |
2 - 5 |
| Ethyl methyl sulphide |
0.4 to 200 |
2 - 5 |
| Diethyl sulphide |
0.4 to 200 |
2 - 5 |
| Methanethiol |
0.4 to 200 |
2 - 5 |
| Ethanethiol |
0.4 to 200 |
2 - 5 |
| 2-propanethiol |
0.4 to 200 |
2 - 5 |
| 1-propanethiol |
0.4 to 200 |
2 - 5 |
| 2-methyl-2-propanethiol |
0.4 to 200 |
2 - 5 |
| Tetrahydrothiophene |
0.4 to 200 |
2 - 5 |
Terpenes
Terpenes are a common impurity found within biogas due to the nature of the biological source material. The presence of trace level terpenes within biomethane cause the scent of typical sulphur odorant additives to be masked, posing a health and safety risk. In addition they are capable of causing degradation of polymeric seal materials used within transmission grid pipelines. NPL provides reference standards containing terpenes within biogas, methane and nitrogen matrices.
Component
|
Amount fraction range (µmol/mol)
|
Relative Uncertainty (%)
|
Matrix
|
| (+/-)-α-pinene |
0.01-10 |
2 - 5 |
Biogas, Methane or Nitrogen
|
| (+/-)-β-pinene |
0.01-10 |
2 - 5 |
| (+)-3-carene |
0.01-10 |
2 - 5 |
| 1,8-cineole (eucalyptol) |
0.01-10 |
2 - 5 |
| Limonene |
0.01-10 |
2 - 5 |
| Isoprene |
0.01-10 |
2 - 5 |
BTEX
Benzene, toluene, ethylbenzene and xylenes are volatile mono-aromatic hydrocarbons found within biogas. NPL provides reference standards containing terpenes within biogas, methane and nitrogen matrices.
Component
|
Amount fraction range (nmol/mol)
|
Relative Uncertainty (%)
|
Matrix
|
| Benzene |
500 - 2000 |
2 - 5 |
Biogas, Methane or Nitrogen
|
| Toluene |
500 - 2000 |
2 - 5 |
| Ethylbenzene |
500 - 2000 |
2 - 5 |
| m+p-xylene |
500 - 2000 |
2 - 5 |
| o-xylene |
500 - 2000 |
2 - 5 |
Ammonia
Ammonia is produced during the anaerobic digestion process and is found within biogas. NPL provides reference standards containing ammonia within biogas, methane and nitrogen matrices.
Component
|
Amount fraction range (nmol/mol)
|
Relative Uncertainty (%)
|
Matrix
|
| Ammonia |
10 - 1000 |
5 - 10 |
Biogas, Methane or Nitrogen
|
Proficiency testing
NPL offers 'on-demand' proficiency testing schemes for biogas composition and impurities.
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